I know we've talked about this before on this forum, and I seem to be one of the minority who would be willing to knowingly spay while pregnant -- at least in theory, since I've never had to make that choice, and only if it were early on in the pregnancy.
It's not that I wouldn't want the kittens to live, or that I don't also think that their lives are precious. But I also know that there's only a finite number of homes out there for all the cats who are already living. Every kitten born and adopted means that another cat or kitten somewhere is going to miss out on a chance at a home, with a high probability of being put to sleep.
I'm really sorry for those kittens, and that they didn't get their own chance at life. But at least they didn't know what was going on or what they were missing. And I believe that because of it, somewhere else, there are a few other already-born cats who will have a chance now.
That's why I said that if I had known, I probably would have had them do it anyway, at least if it were early on. Even though I would have felt awful about it.
But no matter how you feel about it, I think we all agree that vets should tell you before they do it. They shouldn't presume to make the decision for you.